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The interactions of 1/6 <112]{111}[sub γ] slip dislocations in deformation twins with {111}[sub γ] (0001)[sub α2] interphase interfaces, intersecting along both <101][sub γ](30°-type) and <110][sub γ] (edge-type) directions, in duplex Ti-Al alloys after room-temperature deformation in tension, have been investigated by transmission electron microscopy. The dislocation reactions involved in each of these types of interaction have been fully identified by image matching between experimental and computed images. Slip transfer of 30°-type 1/6<112]{111}[sub γ] twinning dislocations across the γ-α[sub 2] interface into 1/3;<1120>{1100}[sub α2] slip dislocations has been confirmed and completely characterized. In addition to this primary slip system a new secondary slip system of 1/3;<1120>{3301}[sub α2] is activated within the [sub α2] phase under conditions of high levels of plastic strain. This new slip system has also been observed to be the favoured route for slip transfer of incoming 30&deg>-type 1/6<112]{111}[sub γ] twinning dislocations when the plane of the γ-α[sub 2] interface deviates significantly from {111}[sub γ] (0001)[sub α2] and the line of intersection is no longer close to <101][sub γ]. For the interaction involving edge-type 1<112]{111}[sub γ] twinning -dislocations with {111}[sub γ] (0001)[sub α2] [sub γ-α2] interfaces, no [sup 6]significant transfer of dislocations into the [sub α2] phase was observed. Instead, stress relief of the incoming twinning dislocation pile-up at the γ α[sub 2] interface occurs via ½<110]{001)[sub γ] slip dislocations 'reflecting' back into the γ phase coupled with the generation of a new twinned γ grain at the γ α2 interface. No dislocation reactions involving c -component dislocations in the [sub α2] phase were observed for any of the interactions investigated. [ABSTRACT FROM AUTHOR]

X-ray incoherent channelling patterns (ICPs) are generated by variations in characteristic X-ray emission rates induced by a systematic scan of incident fast electron beam orientation near low index zone axes. ICP contrast is used to derive relative sublattice site occupancies of alloyed atoms in Al[sub 3]Ti and related intermetallics. Depending on composition and alloying atoms, these have crystal structures of type D0[sub 22] or L1[sub 2]. When V is added to form the D0[sub 22 ]intermetallic Al[sub 3](V[sub 0.6]Ti[sub 0.4]), it is shown that Ti and V share the same sublattice site. The L1[sub 2] structure is stabilized by additions of Cr (which induces the transformation from the D0[sub 22] structure and stabilizes the L1[sub 2] phase). Elements X = Hf, Zr and W were added at the 0.5 at.% level to form separate quaternary alloys of overall composition Al[sub 62]Cr[sub 10.5]Ti[sub 27]X[sub 0.5] with the L1[sub 2] crystal structure. The sublattice site partitioning of these minority atoms is investigated by the formation of X-ray ICPs and subsequent statistical analysis of these patterns, related to atom location by channelling enhanced microanalysis (or ALCHEMI). It is shown that Hf and Zr are accommodated exclusively on Ti sublattice sites whereas W favours the Al sublattice site with about 10% of the alloyed W atoms accommodated on Ti sublattice sites. Cr is shown to partition exclusively onto the Al sublattice site. Contrast from a <110> zone confirms that these minority atoms do not occupy the interstitial site at the body centre position of the L1[sub 2] unit cell. Convergent beam electron diffraction data from the zeroorder Laue zone and higher order Laue zone are shown and discussed for the <100> projection of the L1[sub 2] structure. [ABSTRACT FROM AUTHOR]